Method and device for controlling feed in a centrifugal separator



Jan. 7, I969 HIDEYO UMEDA 3,420,374

METHOD AND DEVICE FOR CONTROLLING FEED IN A CENTRIFUGAL SEPARATOR FiledApril 11, 1967 i :uumm: 43 V I 420 CBF FIQZ 4o 43b 43b l 43 33 42 i 430i 35 a 4| t 4 FIG 4 3o 44- I Fl6.5 v

INVENTOR.

H/DEYO UMEDA R TTORNE Y5 United States Patent 41/23,4s3 US. Cl. 210-7sInt. Cl. B04b 11/02 12 Claims ABSTRACT OF THE DISCLOSURE A detectingdevice for a centrifugal separator capable of detecting the thickness ofa cake in a basket after having reached a predetermined value bydetecting ultrasonic waves emanated upon contact of a detecting leverwith the cake when the cake has grown up to a predetermined thickness.

The present invention relates to a centrifugal separator and moreparticularly to a method and a device for controlling feed of liquid orslurry into the centrifugal separator.

In solid-liquid separating operation using a batch type centrifugalseparator, it has been a common practice to perform the various steps ofthe operation, starting by feeding of slurry and ending "by removal ofseparated solids, in sequence on a continuous basis by means of theso-called sequence control. Although it is customary to use a timer forthe sequence control because, in many instances, the steps in theoperation of a centrifugal separator are carried out in a timedrelation, there may be cases wherein use of a timer for feedingoperation is difficult due to the characteristics of a slurry to beprocessed. More specifically, in processing a mixture of a solid and aliquid by the use of a centrifugal separator, the working ratio of theseparator will be lowered when feeding of the mixture is stopped beforethe cake formed as a result of separation has reached a predeterminedvalue, whereas the centrifugal separator will be overloaded when feedingof the mixture is not stopped even after the amount of the cake hasexceeded a tolerable limit. Furthermore, variation in amount of thesolid substance in each batch will result in lowering of efiiciency inthe succeeding step, e.g. the step of drying the separated solidsubstance. For the foregoing reasons, it is desirable to control feedingof a slurry based on the amount of a cake separated and not by the useof a timer.

In order to attain this purpose, there has been proposed a method inwhich feeding of a slurry is stopped when the slurry has reached apredetermined level, by detecting a drastic change in electricresistance or electrostatic capacity between an electrode fixed interiorof a separation basket and an earthing electrode occurring upon contactof the end extremity of the electrode with the surface of the slurry inthe basket. This method, however, is not satisfactory in that the liquidlevel and the amount of the cake separated vary depending upon thecharacteristics and feeding rate of a slurry being handled. Anotherdrawback of the method described is that maintenance of a device bywhich the method is operated is troublesome because the electrode andthe earthing electrode must be electrically insulated from each othercompletely.

Another device which has been proposed heretofore is one in whichfeeding of a slurry is stopped by the action of a microswitch which isadapted to be actuated by a rocking detector lever provided in a basketin such a manner that it is displaced from its normal position by3,420,374 Patented Jan. 7, 1969 the slurry in the basket when thesurface of the slurry has reached a predetermined level. The device ofthis type, however, has the same drawback as that possessed by thepreceding device using electrodes, since the feeding of the slurry iscontrolled by detecting the liquid level in the basket, and the furtherdrawback that the contruction is rendered complicated due to theexistence of moving parts.

It is, therefore, the primary object of the present invention toeliminate the aforementioned drawbacks of the conventional devices.

It is another object of this invention to provide a method and devicefor controlling feeding of a slurry in accordance with the position of acake surface and not with the level of the liquid in a basket.

It is still another object of this invention to provide a method whereinfeeding of a slurry is stopped by detecting ultrasonic waves emanatedupon contact of the tip end of a lever, disposed in the basket of acentrifugal separator and supported by the casing of the separator, witha cake of solid substance separated in the basket, and a device forpractising the method. The term ultrasonic as used herein is intended toinclude audible sonic.

These and other objects and advantages of the present invention willbecome apparent from the following detailed description when taken inconjunction with the accompanying drawings, in which:

FIGURE 1 is a vertical cross section of a centrifugal separatorillustrating an embodiment of the present invention;

FIGURE 2 is a schematic diagram illustrating an embodiment of the feedcontrol system used in the present invention;

FIGURE 3 is an enlarged cross section showing a detecting unit of thetype using no vibration-preventive rubber; and

FIGURE 4 is an enlarged cross section showing a detecting unit providedwith means by which a detecting lever is moved from an actuatingposition to a nonactuating position immediately after detecting a cakehaving reached a predetermined thickness.

Referring to FIG. 1, a centrifugal separator generally indicated at 1includes a fixedly supported casing 2 and a separation basket 3rotatably mounted within said casing 2. The basket 3 is secured to thetop end of a drive shaft 4, extending through the center of the casing2, by a key or other suitable means, so that it is driven from asuitable power source (not shown) through said drive shaft 4. The casing2 has a feed port (not shown) for a slurry. The slurry introduced intothe basket 3 through the feed port is rotated, for the basket isrotating at high speeds. Thus, the slurry is pressed against acylindrical screen 3a of the basket 3 due to the centrifugal forcedeveloped therein. In this case, a solid substance in the slurry, whichhas a greater mass than the liquid, is gathered in a radially outsideportion of the basket 3 as indicated at 5 in FIG. 1, while the liquidremains in a radially inside portion as indicated at 6 in said figure.When the layer or cake 5 of the solid substance formed in the basket 3has reached a predetermined thickness, supply of the slurry isinterrupted, with the basket 3 rotating continuously. As a result, theliquid only is discharged from the basket 3 radially outwardly throughthe cake 5 which is prevented from moving in a radially outwarddirection by the screen 3a. The liquid discharged from the basket 3conflicts against the peripheral side wall of the casing 2, flowsdownwardly on the side wall and drains to the outside through a drainhole (not shown) in the casing after flowing through a passage 2a formedat the bottom of the casing 2. When the liquid is substantially removedfrom the cake 5 of the solid substance formed in the basket 3, the cakeis scraped down by means of a scraping blade (not shown) while rotatingthe basket 3 slowly and removed from the basket through a discharge port3b in the lower portion of the basket. The construction and operation ofthe centrifugal separator as described above are well known and will notbe described in further detail.

The centrifugal separator according to the present invention is providedwith a detector for detecting the thickness of the cake 5 after havingreached a predetermined value, which detector is generally indicated bynumeral 7 in FIG. 1. The detector 7 includes a housing 9 fitted to acover 8 for the casing 2 of the centrifugal separator and a detectinglever 11 held in the housing 9 through a vibration-preventive rubberbush 10. The detecting lever 11 is extending downwardly from the lowerend of the housing 9 and flexed into L-shape with its end extremityarranged for contact with the surface of the cake 5 in the basket 3 whenthe cake has grown up to a predetermined thickness. The upper end of thedetecting lever 11 is protruding upwardly from the rubber bush and witha piezo-electric unit fixed thereto, said piezo-electric unit 15consisting of a piezo-electric element 12 and electrodes 13 and 14attached to both sides thereof. The electrodes 13 and 14 have lead wires16 and 17 connected thereto respectively.

When the cake 5 has grown up to a predetermined thickness duringoperation of the centrifugal separator 1, the solid substanceconstituting the cake 5 comes in contact with the end extremity of thelever 11, emanating ultrasonic waves. The ultrasonic waves aretransmitted through the lever 11 to the piezo-electric unit 15. As aresult, a voltage is developed in the piezo-electric unit 15 and thisvoltage is taken out through the lead wires 16 and 17 in the form of anelectric signal indicating that the thickness of the cake has reached apredetermined value. The electric signal is amplified in a known mannerto actuate the feed control system and thus the feeding of the slurry isinterrupted.

An embodiment of the control system for controlling feeding of theslurry in response to the electric signal from the piezo-electric unit15 is schematically shown in FIG. 2. Referring to this figure, anelectric signal from the detecting unit 7 is fed to an amplifier 18through a line 19, wherein it is amplified and sent to a hydrauliccontrol valve 21 through a line to act on the same. The control valve21, therefore, is actuated by the output from the amplifier 18 andconnects a hydraulic circuit 22 with a line 23. A pressure oil from apressure source (not shown) is thus led into a shut-off valve 24 toclose the same and consequently the slurry being fed through a line 26is interrupted.

The detecting lever 11 is preferably made of a metal but may be made ofany other material which is capable of conducting ultrasonic waves. Itis also preferable that the detecting lever 11 is shaped into such aconfiguration as to provide a small fluid resistance so as to avoidscattering of the slurry.

In the embodiment described above, the ultrasonic waves generated by therotation of the basket 3 of the centrifugal separator will betransmitted to the detector unit 7 through the casing 2, however theWaves from the casing 2 to the lever 11 will be substantially absorbedby the vibration-preventive rubber bush 10 and extremely attenuated. Therubber bush 10 is not always necessarily used in the position shown butthe same effect may be obtained, for example, by interposing an absorberbetween the cover 8 and the casing 2. Such an arrangement isadvantageous in avoiding rocking of the lever caused by a solidsubstance abutting thereagainst, due to the fact that the lever 11 isfixed to the housing 9 with a high rigidity at the joint.

In handling a slurry of relatively raw solid such as that of sodiumglutamate, the ultrasonic generated upon contact of the cake 5 with thelever 11 generally has an amplitude far larger 1 2 2 1 that generated bythe rotation of the basket 3 and conducted through the casing 2.Therefore, the ultrasonic from the lever 11 is sufficiently detectablewithout using the vibration-preventive rubber.

An embodiment of the detector unit wherein a detecting lever is fixedwithout using a vibration-preventive rubber is shown in FIG. 3. In thisembodiment, the detector unit 30 has a flange 31 for securing saiddetector unit to the cover 8, and a detecting lever 32 similar to thedetecting lever 11 is formed integrally with the flange 31. Provided atthe top end of the lever 32 is a piezoelectric unit 33, similar to thepiezo-electric unit 15, which is mounted thereto by means of a stud 34.A housing 35 is provided integrally with the flange 31 and covers thepiezo-electric unit 33. Electric wires from said piezo-electric unit areled to the outside through an aperture 37 formed in the housing 35.

FIG. 4 shows another form of the detector unit. In this form, apneumatic cylinder 42 having a floating piston 43 therein is fixedlymounted on the top surface of a housing 41 of the detector unit 40 and adetecting lever 44 is carried for rotation with respect to the housing41 and the cylinder 42. A piezo-electric unit 45 is the same as thatshown in FIG. 3.

The piston 43 in the cylinder 42 has a skirt portion 43a having a pairof spiral cam slots 43b provided at the diametrically opposed position.Each slot 43b is engaged with a cam follower pin 42a secured on thecylinder 42. Between the slots 43b, the skirt 43a of the piston 43 isformed with a pair of opposed cam slots 430 (only one of which is shownin FIGURE 4), each of which is engaged with a pin portion (not shown)formed at each end of a transverse member 44a fixed on the lever 44. Theslots 430 are similar to the slots 43b but their direction of spiral isreverse to that of the latter, so that, when the piston 43 is movedvertically, the lever 44 is rotated. The cylinder 42 has ports 49 and 50connected thereto through which a compressed air is introduced into ordischarged from the chambers formed above and below the piston 43.

In this embodiment, when an ultrasonic is generated upon contact of theend extremity of the lever 44 with the cake formed in the basket of thecentrifugal separator, indicating that the cake has grown up to apredetermined thickness, a compressed air is introduced through, e.g.the port 49 depressing the piston 43 downwardly. Then, the lever 44 isrotated about its axis whereby the tip end of the lever 44 is moved fromthe operative position in which it is in contact with the cake withinthe basket, radially inwardly into a position in which it will not comein contact with the cake 5. Thus, it will be understood that the tip endof the lever 44 is not contacted by the cake 5 during the separatingperiod after interruption of the feeding, with the result that wearingof the detecting lever can be reduced remarkably.

Although the present invention has been described and illustrated indetail in terms of the specific embodiments, it is of course to beunderstood that these embodiments are only illustrative and are in noway restrictive in respect of details of the construction andarrangement.

What is claimed is:

1. A method of automatically controlling feeding of a slurry into acentrifugal separator by detecting a cake of a solid substance havinggrown up to a predetermined thickness in a rotary basket in saidcentrifugal separator, said method comprising the steps of converting anultrasonic wave generated upon contact of the tip end of a detelctinglever, fixed in a predetermined position in the centrifugal separator,with the solid substance into an electric signal and amplifying saidsignal to actuate slurry feed control means.

2. A centrifugal separator comprising a fixed casing, a separationbasket rotatably mounted in said fixed casing, means to rotate saidbasket, means to feed a slurry into said basket and means to detect theamount of a cake formed of a solid substance in the slurry uponseparation from a liquid in the basket and having reached apredetermined value, said detecting means including a housing mounted ona fixed portion of the centrifugal separator and a detecting memberretained in said housing, one end of said detecting member beingpositioned at a location at which it is engageable with said cake assaid cake has grown up to a predetermined thickness, and said detectingmember being combined with means to convert ultrasonic waves generatedupon contact of said one end of the detecting member with said cake intoan electric signal and provided with means to control said slurry feedmeans in response to said electric signal.

3. A centrifugal separator according to claim 2, in which saidconverting means is a piezo-electric unit having a piezo-electricelement.

4. A centrifugal separator according to claim 2, in which the housing ofsaid detecting means is mounted on the top cover of said fixed casingand said detecting member consisting of a L-shaped lever extendingdownwardly from the housing of said detecting means and then radiallyoutwardly with its tip end located at a point a predetermined distancespaced radially inwardly from a cylindrical screen in said separationbasket.

5. A centrifugal separator according to claim 4, in which said L-shapedlever is supported by said housing through the intermediary of buttermeans.

6. A centrifugal separator according to claim 4, in which said L-shapedlever is fixed directly to said housing.

7. A centrifugal separator according to claim 4, in which said L-shapedlever is arranged within said housing so as to be rotatable about itsvertical axis and there being provided means to turn said lever afterthe ultrasonic waves are generated upon contact of the tip end of saidlever with the cake and to move the tip end of said lever into aninoperative position in which it will not come in contact with the cake.

8. A centrifugal separator according to claim 7, in which said means tomove said lever into the inoperative position comprises a cylinder fixedto the housing of said detecting means, a piston disposed axiallymovably and rotatably in said cylinder, cam means for rotating the leverupon axial movement of the piston, and means to selectively introduce acompressed air into chambers formed within the cylinder at both sides ofsaid piston.

9. A detecting device for detecting the amount of solid substanceseparated from a slurry and having reached a predetermined value in acentrifugal separator comprising a separation basket, said devicecomprising a detecting member capable of transmitting ultrasonic waves,a housing for retaining and suspending said detecting member into saidbasket, the distal end of said detecting member being positioned at alocation at which it is engageable with said solid substance as saidsolid substance has grown up to a predetermined thickness in saidbasket, means combined with said detecting member to convert theultrasonic waves transmitted to said detecting member upon contact ofthe distal end of said ,member with said solid substance, into anelectric signal, and means controlling the fiow of said slurry to saidcentrifugal separator responsive to said electric signal.

10. A detecting device according to claim 9, in which said detectingmember is an L-shaped lever extending from one end of said housing andsaid converting means includes a piezo-electric unit having apiezo-electric element.

11. A detecting device according to claim 10, in which said lever issupported by said housing through the intermediary of buffer-means.

12. A detecting device according to claim 10, in which said lever isfixed directly to said housing.

References Cited UNITED STATES PATENTS 2,524,579 10/1950 Taylor 34026l X2,912,110 11/1959 Stoltenberg 21086 X 3,044,625 7/1962 Smith et al.210-86 3,141,846 7/1964 Laven 210-86 X REUBEN FRIEDMAN, PrimaryExaminer.

J. L. DE CESARE, Assistant Examiner.

US. Cl. X.R.

